The present invention relates to a thin film semiconductor substrate for a display device and its method for manufacturing incorporated in an active matrix-type liquid crystal display device used mainly for a direct viewing type display apparatus or a projection-type display apparatus.
A conventional prior art method for manufacturing a thin film semiconductor substrate to be incorporated in the active matrix-type liquid crystal display device is composed of the following processes:
(A) A process of making a single crystal semiconductor layer formed on a single crystal semiconductor substrate containing an insulating oxide film between them into a thin film semiconductor circuit layer by means of high resolution semiconductor processing;
(B) A process of sticking together the thin film semiconductor circuit layer and a support substrate with an adhesive layer between them; and
(C) A process of removing the single crystal semiconductor substrate by means of grinding or etching while leaving the oxide film layer of the single crystal semiconductor substrate and the thin film semiconductor circuit layer.
However, the above-mentioned conventional manufacturing method has the following problems.
In the process of removing a single crystal semiconductor substrate by means of the former manufacturing method, first, a thickness of 625 .mu.m is shaved off to about 125 .mu.m by means of grinding and next, the rest of it is removed by means of anisotropic etching while using the oxide layer as a stopper layer. In this case there is a problem such that before the etching is finished a thin film semiconductor circuit layer is destroyed by stripping off the thin film semiconductor circuit layer from its circumference part, since the etching agent penetrates into the boundary face between the support substrate and the adhesive layer from the circumference and erodes the adhesive layer as the etching proceeds and the thickness of the single crystal semiconductor substrate becomes reduced. Furthermore, where the difference in levels of a pattern of a thin film semiconductor circuit layer is large, there is also a problem that according to the progress of the etching and as the thickness of the single crystal semiconductor substrate becomes reduced, the stress concentrated on the level difference part of the pattern, which has been suppressed by the thickness of the single crystal semiconductor substrate until that time, becomes released, and exfoliation of the thin film semiconductor circuit layer begins at this point.
An object of the present invention is to solve the above-mentioned prior art problems and to provide a new method for manufacturing a thin film semiconductor substrate by removing a single crystal semiconductor substrate while leaving an oxide film layer and a thin film semiconductor circuit layer after sticking together a support substrate and the thin film semiconductor circuit layer formed on the single crystal semiconductor substrate and containing the oxide layer therebetween.